1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor light-emitting device including a vertical cavity structure.
2. Description of the Related Art
A surface-emitting laser diode differs from an edge-emitting laser diode of the related art in that the surface-emitting laser diode emits a light in a direction orthogonal to a substrate, and allows multiple devices to be arranged in a two-dimensional array on the same substrate. Thus, the surface-emitting laser diode has attracted attention in recent years as a light source used for a digital copying machine and a printer.
As shown in FIG. 16, for example, this type of surface-emitting laser diode includes a vertical cavity structure by stacking, on a substrate 110, a lower DBR layer 111, a lower spacer layer 112, an active layer 113, an upper spacer layer 114, a current confinement layer 115, an upper DBR layer 116, and a contact layer 117 in this order from the substrate 110 side. A columnar mesa 118 is formed in an upper part of the vertical cavity structure, specifically, in a part of the lower DBR layer 111, the lower spacer layer 112, the active layer 113, the upper spacer layer 114, the current confinement layer 115, the upper DBR layer 116, and the contact layer 117. An upper electrode 121 is formed on an upper surface of the mesa 118, and a lower electrode 122 is formed on a rear surface of the substrate 110. In addition, FIG. 16 illustrates an example of a cross sectional configuration of a surface-emitting laser diode 100 of the related art.
The mesa 118 is, for example, formed as will be described below. First, the vertical cavity structure is formed by stacking the lower DBR layer 111, the lower spacer layer 112, the active layer 113, the upper spacer layer 114, a layer to be oxidized 115D, the upper DBR layer 116, and the contact layer 117 in this order on the substrate 110. Then, a circular mask layer M10 is formed on the upper surface of the contact layer 117 (FIG. 17). In addition, the layer to be oxidized 115D will become the current confinement layer 115 through an oxidation process, which will be described later.
Next, by a dry etching method, the upper part of the vertical cavity structure is selectively etched while using the mask layer M10 as a mask, thereby forming the columnar mesa 118D. The layer to be oxidized 115D is selectively oxidized from the side face of the mesa 118D, for example, by a high-temperature oxidation treatment in a water-vapor atmosphere (FIG. 18). Therefore, in the layer to be oxidized 115D, a region from the side surface to a predetermined depth becomes an oxidation region (insulating region), which serves as a current confinement region 115A, and a region further deep from the oxidation region becomes a non-oxidation region, which serves as a current injection region 115B. In this manner, the current confinement layer 115 composed of the current confinement region 115A and the current injection region 115B is formed.
Typically, the layer to be oxidized 115D is made of a material, which is most easily oxidized in the vertical cavity structure, such as AlGaAs with high Al composition ratio. However, each of the lower DBR layer 111 and the upper DBR layer 116 included in the vertical cavity structure generally has a stacked structure by alternately stacking a low refractive index layer with relatively high Al composition ratio and a high refractive index layer with relatively low Al composition ratio. The low refractive index layer included in each of the lower DBR layer 111 and the upper DBR layer 116 is oxidized with relative ease. That means, in the vertical cavity structure, there are still other layers except the layer to be oxidized 115D, which are easily oxidized. This causes that the layers which are oxidized with relative ease, such as the low refractive index layer included in each of the lower DBR layer 111 and the upper DBR layer 116, are also oxidized in the case of the excessive oxidation in the oxidation process for the layer to be oxidized 115D (refer to oxidation portions 111A and 116A in FIG. 18). As a result, in not only the current confinement layer 115 but also other layers except the current confinement layer 115 in the vertical cavity structure, there is a risk that deformation caused by volume shrinkage during the oxidation occurs and thus mechanical destruction is produced. Further, various impurities such as oxygen are included in an interface (an oxidation front) between the oxidation region and the non-oxidation region so that the oxidation front is in an unstable state. For this reason, damage starting from the oxidation front may grow with time, and there is a risk that a device lifetime decreases since the other layers except the layer to be oxidized 115D in the vertical cavity structure are also oxidized.
In order to solve this issue, for example, in Japanese Unexamined Patent Publication No. 2004-179640, proposed is a method in which an In-containing layer (InAlGaAs) with a lattice constant larger than those of surrounding layers is provided adjacently to a current confinement layer so that the deformation caused by the volume shrinkage during the oxidation is compensated. For example, in Japanese Unexamined Patent Publication No. 2003-158340, proposed is a method in which an oxidation confinement diameter of a current confinement layer is set larger than a certain level so that stress applied on the active layer due to the deformation caused by the volume shrinkage during the oxidation is suppressed.